Network, generic (extended)

U3562 Cathode Bypass Valve

Check engine lightOn
EmissionsNot relevant
Drive cycleRequired
Limp modePossible

Unlike U3561, this code concerns how the cathode bypass valve itself behaves: it does not reach or hold the opening the controller asks for, for instance because it sticks. A Toyota patent shows why a valve stuck shut is serious. While a cold stack is warmed by deliberately inefficient generation, bypass air is supposed to thin out hydrogen in the exhaust; if ice holds the valve closed, all of that air enters the stack, which then produces more power than intended. Toyota spots this from compressor outlet pressure above a limit or from stack current straying from its command, then opens the backpressure valve and slows the compressor. A valve stuck open costs stack pressure instead, as Nissan notes. No maker publishes U3562; that stuck air valves switch on the MIL is documented by Toyota for the Mirai (T-SB-0043-23).

Likely causes

Valve frozen in place after a cold soak
Valve sticking from deposits or wear
Actuator too weak or gear damaged
Position feedback reading wrong, valve itself fine

Symptoms

  • Fuel cell system warning, MIL on
  • Reduced power or failed start in frost
  • Unusual compressor or air noise

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€300–1,500
Time1–4 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

cathode bypass valve

Related codes

U3561U3563U355FU3559

References: patents.google.com, patents.google.com, static.nhtsa.gov.